1. Field of the Invention
The present invention relates generally to devices for coating small pieces of product with liquid substances, and more specifically to a large scale batch tumbler for coating liquids onto particulate core pieces.
2. Description of Related Art
Almost every sector of contemporary society is increasingly organized around the principles of convenience and economy. In the food industry, one of the more recent innovations to promote these principles in the presentation and preservation of food products is the "freeze-coated pour and store" concept. In this method, small sized food products, such as cooked pasta, meat or vegetables, are rapidly frozen using a cryogenic material, such as liquid nitrogen or liquid carbon dioxide, and then surface coated with a liquid sauce. The temperatures under which the process is conducted cause the sauce to freeze on contact with the product. Small amounts of product can then be individually packaged by the processor for sale to the end consumer.
The pour and store concept has gained wide general acceptance by processors and consumers alike. For processors it fulfills the objective of producing value added products to offer the retail and food service marketplace. That is, the combination of food pieces with a sauce freeze-coated to the surface has a value surpassing the combined cost of the core product and the sauce. For the consumer, the freeze coating method, when effectively executed, prevents product clumping and instead maintains the particulate product in discrete pieces, therefore permitting the consumer to select any amount of the packaged product desired for eating and return the remainder to its package for continued freezing. More significantly, the consumer has a preprepared entree or side dish having more complex flavors, textures, and nutritional benefits than would be provided by either the core product or sauce alone. When the finished product is reheated, the resulting meal is an appealing combination of sauce and core product in the proper proportions each time.
However, coating liquids onto core pieces by first freezing the core pieces and then spraying on liquid is an exacting and unforgiving process. The core pieces must be evenly frozen to a specifically controlled temperature for the liquid to adhere properly. Additionally, the liquid spray must be metered out within very small tolerances and then precisely directed onto the frozen core pieces to result in an even coating on all core pieces. Any error in spray discharge rate or coverage area will result in uneven coating or, worse yet, product clumping.
To avoid the foregoing problems, a truly effective freeze coating method requires that the system be designed to keep the product under constant motion within the spraying field while it is exposed to cryogen and sauce. Several freeze coating devices have been proposed to meet these needs, including that disclosed in U.S. Pat. No. 5,911,827, recently issued to Heller.
The '827 patent teaches an apparatus comprising a horizontally positioned rotatable drum having a generally cylindrical profile with tapered ends. The drum is driven by mechanical rollers that engage the drum surface directly. At one end of the drum is a first opening, which provides an inlet for filling the drum with product before processing and also as an outlet for the discharge of gaseous coolant during the operating process. Because cryogenic material evaporates so quickly, the discharge must be rapid and intensive and requires an exhaust pipe having a cross sectional area essentially that of the first opening and further assistance from a blower mounted on the exhaust pipe. At the opposite end is an opening for discharge of the finished product. Cryogen is introduced through the first opening and into the drum during processing through either a CO.sub.2 "snow pipe" or a pipeline terminating in nozzles for the emission of liquid nitrogen. Using a second nozzle, coating sauce is also introduced through the first opening.
As with other freeze coating systems of this type, the '827 patent discloses a device with several limitations. Systems in this class are modifications of older vacuum tumblers in which control of product movement is not directed to each piece of product; rather, control of movement is directed to the batch as a whole. Characteristically, tumblers of this type have long drum shapes with tapered ends and generally straight mixing vanes which move and contain product generally in the central area of the drum. While the disadvantages of these systems are not self-evident, they become apparent when the systems are operated with a variety of kinds of product. Taking the model disclosed in Heller as an example, the disadvantages may outlined as follows:
1. The drum is too long and provides inadequate control over the location of the moving core pieces as the drum turns; PA1 2. The vane system is designed to tumble core product without mixing the core pieces to ensure even coating; PA1 3. The cryogenic gas is extracted at the same end that the cryogen and coating liquid enter the drum. In consequence, rapidly evaporating and expanding cryogen flows past the spray nozzles at violently high flow rates, disrupting precision of the spray pattern of both cryogen and coating liquid. As a result, both chilling and coating are uneven; PA1 4. Attempting to correct the immediately preceding problem by extending the cryogen and coating liquid discharge nozzles or probes more deeply inside the go drum is a remedy with its own problems: PA1 5. The drum is rotated by wheels directly under the body of the drum and depend upon friction between the tires and the drum. Due to the low temperatures inside the drum during processing, ambient atmospheric moisture condenses and freezes on the outside surface of the drum causing the drive wheels to slip on the drum surface. This results in erratic and unreliable speed control of the rotating drum and adversely affects the coating of core pieces. PA1 1. The coolant does not contact the steel drum interior during the chilling process; thus product will not freeze to the drum. PA1 2. The coolant covers each core piece evenly because each piece is passed under cryogenic spray in a highly controlled manner. Every core piece is continually moved within the drum and coating field in a manner that ensures it is frozen at or near the same temperature as every other core piece and is subjected to a volume of coating spray in substantially the same amount as every other core piece; thus, liquid coating freezes to the core pieces evenly, and there is no clumping of the product. The core pieces are individually quick frozen and, if desired, the product may be 100% coated.
a. the piping of the coating liquid has too long a length and can freeze the liquid inside the probe piping; and PA2 b. the mechanism for removing the long probe piping from the machine after the core product is loaded requires an unreasonable amount of space in front of the tumbler when the probes are extracted, thus interfering with factory operations.
It would be desirable, therefore, to provide an apparatus and method for coating liquids onto core pieces that overcomes the above-described limitations.